The present invention relates to a conveyor that blows plastic bottles along a flow path, and more particularly to an air conveyor that conveys the bottles at substantially constant speed and substantially maintains small spacing between successive plastic bottles along the conveyor path.
An air conveyor is useful for the rapid transport of plastic bottles between work stations as, for example, between a storage station and a bottle-filling station. Typically, the known air conveyor includes a pair of flanges spaced to define an elongated slot between them, and a series of air ducts on opposite sides of the slot. Plastic bottles are formed with annular rims adjacent the tops of their necks. With the bottle necks extending through the slot and the rims overlying the spaced flanges, the bottles are suspended from the flanges and hang below the slot. Pressurized air from the ducts is directed in streams toward the bottles. The bottles move through the slot because of the force of the air streams against the bottles. Preferably, the bottles are conveyed in closely spaced succession.
In at least some of the conventional air conveyors, the air is directed through a plenum within a channel and against the tops of the bottles above the annular rims. This results in turbulence of air emerging through the elongated slot causing fluttering of the bottles and left to right wobbling as they are blown. Frequently, this wobbling will cause the bottles to wedge against one another. Often, side rails must be employed alongside the bodies of the bottles to restrict wobbling.
The known air conveyors for plastic bottles are also deficient because once the bottles accumulate, the force of air required to move the slug (accumulated bottles) as a group must be high to overcome the drag. Consequently, as single or spaced bottles are conveyed by this air, the bottles accelerate to high velocity. This high acceleration is detrimental because the bottles collide with other bottles being conveyed or accumulated downstream. More significantly, such accelerated bottles impact with downstream bottles waiting at a work station, such as ahead of a labeler that is generally set to operate at a constant moderate speed. Conversely, if the force of air is reduced to prevent high acceleration of single or random bottles and therefore to prevent high impact, the reduced air flow will be inadequate to move the slug (accumulated bottles). In the prior art, much has been done in attempts to control the force of air, such as modulation of the blower speed, which requires motor speed controls. However, reaction time in depleting the air stored in the plenum as well as in replenishing air blown within the plenum is rather slow compared to the more immediate response required in high speed production lines. In other prior art conveyors, louvers have been installed in the walls of the plenum in an effort to control the speed of single (random) bottles while applying greater force against the slugs. However, since accumulated slugs can and do occur randomly at any place along a given conveyor span, the complexity of such applications becomes neither economical nor practical.